In an important subset of antenna subsystem applications, it is often desired to support both high-gain (e.g., generally narrow beamwidth) and lower gain (generally broader beamwidth/coverage) functions. For example, when communicating with a remote mobile (e.g., airborne) terminal at or near the maximum range, it is desirable to provide the narrowest (highest gain) antenna pattern attributes in order to support the highest possible data rates. In such “maximum range” cases, the “target” (e.g., a remote terminal) is generally moving at a low angular rate (due to its distance from the “user” (e.g., a local terminal) and therefore the narrow nature of the antenna beam does not present a challenge in terms of the ability of the user to “track” the (moving) remote terminal.
Conversely, when operating at or near the minimum range, the required gain is significantly reduced (due to the diminished range between user and remote terminals) while the angular tracking rate is often dramatically increased (due to the near in location and geometry of the fixed user and moving remote). A broader (lower-gain, but easier to track) antenna pattern is generally preferred in the latter (minimum range) case while a narrower (high-gain, but more difficult to track) antenna pattern is preferred in the former case.
Similarly, in systems which must first acquire a target (e.g., a remote user) before tracking, it is often desirable/advantageous to use a broader antenna beam pattern in order to perform the acquisition function (thereby better accommodating a generally poorer a priori knowledge of the exact target location and pointing angles) before switching to a narrower (higher-gain) “tracking” antenna pattern once the initial acquisition is successfully completed.
The aforementioned communication link scenarios and problem statements are very similar in the cases of typical radar and electronic warfare (i.e., “jamming”) systems which also require both maximum range (minimum angular rate) and minimum range (maximum angular rate) scenarios as well as (wide-beam) “acquisition” and (narrow-beam) “tracking” modes. All share a common benefit from the antenna subsystems ability to provide both selectable narrow- and broad-beam modes.
In a subset of the aforementioned cases, it may be desirable to support different antenna polarization properties such as opposite senses of circular polarization (“left-hand” and “right-hand”) for the two selectable antenna pattern modes. In addition, it is often desirable to provide specific tailored antenna pattern characteristics in the “switched” beam pattern, including selective null-filling (to ensure constant communication), alternate or offset pointing angles (to accommodate varying target geometries), and/or alternate frequency bands of operation (for example, to support switchable Transmit and Receive operation).
Conventional means for realizing the desired dual switchable antenna beam (with dual-polarization, as an option) capabilities include use of two distinct antennas, using a switchable planar array antenna, or using an electronically-scanned antenna.
The “two distinct antennas” approach utilizes two distinct standalone antennas, each tailored to the desired beam properties. A mechanical or electronic switch is then employed to allow for “selection” of the desired antenna beam (antenna subsystem). The resultant “two-antenna” system is bulkier, more expensive, and (in some cases, due to the requisite switch) less capable in terms of power-handling when compared to a single VICTS antenna.
Regarding the switchable planar array antenna, a single planar array antenna is partitioned into two separate antenna apertures which may be switched via an array-mounted switch. This method suffers from the same drawbacks as the aforementioned two distinct antennas solution.
Finally, the electronically-scanned antenna (ESA) can include discrete phase (and in some cases, amplitude) control of individual radiating elements. This control can be employed to selectably switch between narrow and wide beam patterns. However, the added complexity, size, weight, power, and costs of an ESA implementation as compared to a VICTS is significant.